In the field of construction, it is often necessary to ascertain the elevation of a site or of a feature of a building, bridge or any other structure being constructed. When designing a construction project, engineers and architects prepare blueprints indicating the relative elevation of various features, including the elevation of the sub grade, that is, the surface of earth or rock leveled-off to receive a foundation. Accurate elevation measurements are critical to ensure the proper completion of a project.
A common instrument used to measure elevations comprises a single telescopic lens mounted on a tripod base. To measure elevations, the instrument is first placed on a fixed and unalterable position somewhere in the construction site. By adjusting each of the tripod legs, the instrument is calibrated to assure that it is perfectly level with a horizontal plane. One operator then places a reference ruler having spaced measurement marks on top of a reference point of known elevation. The reference ruler may include an adjustable marker. A second operator points the telescope at the measurement ruler and notes or marks the measurement of the ruler, determining the elevation of the horizontal plane of sight of the telescope. Once this horizontal plane of sight is determined, the instrument is swiveled to intersect a vertical axis aligned at a second location of unknown elevation. By having the first operator place the measurement ruler at this second location, the second operator can then note the ruler's measurement and calculate the elevation difference of the second location with respect to the reference point.
Two operators are necessary to operate the tripod telescope instrument, one to operate the tripod-mounted telescope and one to move the measurement ruler along the construction site. If at any time the adjustment on the tripod-mounted telescope is disturbed, either in its alignment to the horizontal plane or on its elevation, an error will occur that will be transferred to all other points in the construction site. Furthermore, the ability of the tripod telescope to measure height differences is limited to the ability to position the ruler within the line of sight of the instrument. Points having heights that differ more than a length of the measurement ruler or are hidden from the line of sight cannot be measured directly.
Other known methods and apparatus for measuring elevations include the use of a laser to triangulate the desired elevation of the site. However, the laser equipment is generally more costly than the traditional telescope. Laser equipment is fragile and complex and may prove to be too expensive for smaller operations. A need remains for a cost-effective apparatus and method for measuring elevations. The desired apparatus would preferably minimize measurement error and allow use by a single operator.